A display capacity of a liquid crystal display device using a liquid crystal display has been recently increased.
In a simple matrix structured liquid crystal display device employing a multiplex driving system, a contrast is dropped or a response speed is reduced as the speed of a time sharing is increased. Accordingly, if the liquid crystal display device has about 200 scanning lines, it is difficult to obtain a sufficient contrast.
Accordingly, there has been employed an active matrix system liquid crystal display panel having switching elements in each pixel to remove such drawbacks.
In the active matrix system liquid crystal display system, there are two types, one is a three terminal system employing thin film transistors (hereinafter referred to as "TFT") as switching elements and the other is two terminal system employing nonlinear resistors. The two terminal system is superior to the three terminal system since the former is simple in structure and a method of manufacturing thereof.
A diode type, a varistor type, a thin film diode (hereinafter referred to as "TFD") type and so on are developed as the two terminal system.
Among these types, the TFD type is simple in structure and has few manufacturing steps.
Further, the liquid crystal display panel is required to display with high density and high definition, and the switching elements require reduction of the area they occupy.
As a means for permitting the liquid crystal display panel to display with high density and high definition, a photo-lithography technique and an etching technique which are micro processing techniques in semiconductor production techniques are used. However, even if such semiconductor production techniques are employed, it is very difficult to realize a large area processing with low cost.
The structure of a conventional liquid crystal display device having a switching element which efficiently makes the area larger with low cost will be now described with reference to FIG. 45 which is a plan view showing an example of a conventional liquid crystal display device, FIG. 47 which is a plan view enlarging a part thereof and FIG. 46 which is a cross sectional view taken along the line X--X in FIG. 45.
The liquid crystal display device comprises, as shown in FIG. 47, a first substrate 1, a second substrate 11 which are made of a transparent material and oppose each other by way of a spacer 17 at a certain gap, and a liquid crystal 16 which is filled between the first and second substrates 1 and 11.
A lower electrode 2 and a signal electrode 4 are disposed on the first substrate 1 as a first electrode, and a nonlinear resistor layer 3 is provided on the lower electrode 2. Further, an upper electrode 6 as a second electrode is provided on the nonlinear resistor layer 3 so is to overlap, thereby constituting a nonlinear resistor 9. The upper electrode 6 as the second electrode extends from a display electrode 7 as shown in FIG. 46, and a part of the upper electrode 6 also serves as the display electrode 7.
The nonlinear resistors 9 and the display electrodes 7 are disposed in a matrix shape.
A black matrix 12 is disposed on the second substrate 11 at a part confronting the first substrate 1 as shown by the hatched line in FIG. 46 for preventing leaking of light from gaps defined in the display electrodes 7 disposed on the first substrate 1. That is, the black matrix 12 is disposed on a non-display portion as a shading portion.
An opposed electrode 13 is disposed on the second substrate 11 in a belt shape by way of an interlayer insulating film 14 so as to oppose the display electrode 7 as shown in FIG. 47 so that the opposed electrode 13 is not short circuited, without contact with the black matrix 12.
In FIG. 46, the lower electrode 2 and the signal electrode 4 serving as the first electrode, and the upper electrode 6 and the display electrode 7 serving as the second electrode, disposed on the first substrate 1, are shown by broken lines, wherein the illustration of the nonlinear resistor layer 3 is omitted, and the black matrix 12 and the opposed electrode 13 under the second substrate 11 are shown by solid lines.
The lower electrode 2 disposed on the first substrate 1 extends from the signal electrode 4 so as to constitute the nonlinear resistor 9, and the lower electrode 2 serving as an overhanging region overlaps the upper electrode 6 to constitute the nonlinear resistor 9.
The signal electrode 4 as the first electrode and the display electrode 7 as the second electrode are spaced at a certain gap d as shown in FIG. 46.
The display electrode 7 is disposed to overlap the opposed electrode 13 by way of the liquid crystal 16, thereby forming pixel portions of the liquid crystal display panel.
The black matrix 12 is provided to overlap a region forming the display electrode 7 to a given amount, thereby serving to prevent leaking of light from a peripheral region of the display electrode 7.
The liquid crystal display device performs a given image display owing to the change of transmittance of the liquid crystal 16 in a region where the black matrix 12 is not provided on the display electrode 7.
Further, orientational films 15 and 15 are provided between the first substrate 1 and the second substrate 11 at parts confronting the first substrate 1 and the second substrate 11 as processing layers for regularly aligning molecules of the liquid crystal 16.
As shown in FIG. 45, the signal electrodes 4 in M rows are disposed on the first substrate 1 while the opposed electrodes 13 or data electrodes in N columns are disposed on the second substrate 11 so as to structure the liquid crystal display device having a display region 18 formed of a matrix in M rows and N columns as shown by one dot chain line.
The display electrodes 7 are provided at an intersection between the signal electrodes 4 in M rows and the opposed electrodes 13 or data electrodes in N columns, and the nonlinear resistors (TFD in this example) 9 are provided between the signal electrodes 4 and the display electrodes 7.
An anode oxide electrode (anodizing electrode) 5 for connecting the signal electrode 4 in M rows with each other is disposed on the first substrate 1, and connecting electrodes 8 for connecting the signal electrodes 4 with an external circuit are provided at a portion opposite to the anode oxide electrode 5.
In such a manner, the signal electrodes 4 in each column are connected to each other by the anode oxide electrode 5, and the lower electrodes 2 connected to the signal electrodes 4 are at once subject to an anodic oxidation treatment so as to form the nonlinear resistor 3 on the surface of the lower electrodes 2 (FIG. 47), but the signal electrodes 4 in each column are separated from and independent of each other upon completion of the anodic oxidation treatment.
Accordingly, as shown in FIG. 45, the anode oxide electrode 5 has a cut portion 62 which extends outside of a separation line 34 (shown by a broken line) of the first substrate 1 by a length L, and the anode oxide electrode 5 is cut along the separation line 34 upon completion of the anodic oxidation treatment, so that the anode oxide electrode 5 and the cut portion 62 are separated from the first substrate 1.
However, it is necessary to provide the cut portion 62 so as to separate the anode oxide electrode 5 from the signal electrode 4. Accordingly, the anode oxide electrode 5 requires such a sizes that it can be bent by fingers of an operator after the separation line 34 is perforated, which causes a problem of wasting material of the cut portion 62 involved in bending and cutting the cut portion 62.
Further, in a step of separating the cut portion 62 from the signal electrode 4, there is a possibility that the nonlinear resistor 9 is deteriorated in characteristics by static electricity.
Since the end surface of each signal electrode is exposed at the cut part of the first substrate 1, there is a possibility that a short circuit occurs between a plurality of signal electrodes owing to adhesion of dust and moisture.
There is a possibility that the nonlinear resistor is deteriorated in characteristics and damaged depending on time when the cutting step of the anode oxide electrode 5 is taken.
It is impossible to disperse static electricity which locally occurs when the anode oxide electrode 5 are separated from each other during the orientation process for aligning the liquid crystal regularly, which is a treatment for processing the first substrate 1 having the nonlinear resistor 9 to be used for the liquid crystal display device, and during the conveyance or inspection of the liquid crystal display device.
Accordingly, there is a possibility that the nonlinear resistor 9 is deteriorated in characteristics or damaged when an excessive voltage is applied to the nonlinear resistor 9.
Further, it is possible to prevent the nonlinear resistor 9 from being deteriorated in characteristics and damaged by connecting the anode oxide electrodes with each other during the inspection of the liquid crystal display device.
Still further, it is possible to easily inspect the liquid crystal display device since the voltage can be applied to the display electrodes 7 by merely applying the voltage to the anode oxide electrodes 5 which are connected to each other during the inspection step of the liquid crystal display device.
It is required that the contaminant material does not enter between mounting electrodes and a conductive paste before ICs are mounted on the substrate, particularly when the external circuit is mount(ed on the first substrate 1 forming the nonlinear resistor 9, for example, when the ICs, which can be mounted with high density, are mounted on the substrate using a conductive adhesive by a chip on glass (COG) mounting method.
Accordingly, in a structure where the cut portion is defined in the first substrate 1 and the anode oxide electrode is formed on the cut portion, and the cut portion is cut upon completion of the anodic oxidation treatment to thereby separate the anode oxide electrode from the signal electrode as described above, the material is wasted and above-mentioned various demands cannot be satisfied.
Consequently, it is a first object of the invention to provide a liquid crystal display device capable of easily removing a part of the anode oxide electrode by an etching treatment upon completion of the aforementioned various steps, so as to permit the signal electrodes to be independent of each other, thereby preventing the nonlinear resistor from being deteriorated in characteristics and damaged owing to static electricity which occurs during a fabricating step of the nonlinear resistor or during the succeeding steps for manufacturing the liquid crystal display device, and reducing defects of the nonlinear resistor so as to stabilize the characteristics of the nonlinear resistor.
It is another object of the invention to dispense with a part such as a cut portion shown in FIG. 46, which is to be wasted, and to effectively utilize a part which remains after the signal electrodes for the anode oxide electrode used in the anodic oxidation treatment are separated from the anode oxide electrode.
Further, the liquid crystal display device having the aforementioned conventional nonlinear resistors has signal electrodes made of a metal film, and the initial signal electrode and the final signal electrode are the same in wiring width thereof. Accordingly, there is a problem that the signal electrode is hard to repair if poor etching occurs at a part of the signal electrode.
Further, in case that the signal electrode is used as a part of the anode oxide electrode, the anode oxide film cannot be formed if the signal electrode is broken. Still further, it is necessary to form the anode oxide electrode 5 as wide as possible so as to uniformly form an anode oxide film.
Still further, when the transparent conductive film is used as the display electrode, a short circuited part between the signal electrode and the display electrode cannot be easily detected since the display electrode is transparent even if the signal electrode and the display electrode are electrically short circuited owing to poor etching of the transparent conductive film.
Further, as for the TFT element, there is a possibility of occurrence of the breakage of the anode oxide electrode or an electric short circuit between the signal electrode (gate electrode or source electrode) and the transparent display electrode like the TFD element in case that anode oxide film of the gate electrode is used as the gate insulating film utilizing the gate electrode as the anode oxide electrode.
Accordingly, it is still another object of the invention capable of surely and uniformly forming an anode oxide film serving as the nonlinear resistor layers of the nonlinear resistors using the signal electrode as a part of the anode oxide electrode, of easily repairing a poorly etched part when the poor etching occurs in a part of the signal electrode, and of easily detecting a short circuited part when there occurs an electric short circuit between the display electrode of the transparent conductive film and the signal electrode or the anode oxide electrode.